Emergency services were called at 1.05pm to Macandrew Rd, South Dunedin, where the sole occupants of both vehicles received moderate injuries.
A witness said he saw the driver of a station wagon get out of the vehicle and ask for help, before collapsing on the road.
The 20-year-old man was treated by an advanced paramedic from St John and firefighters, and remained on the road until an ambulance arrived at 1.40pm to take him to Dunedin Hospital.
The 64-year-old driver of the other vehicle, who was removed from his vehicle by firefighters, was also treated by the advanced paramedic, before being taken to hospital in the same ambulance.
A St John spokeswoman said care of the patients was not compromised by the delayed arrival of the ambulance, which had been attending another emergency.
"An advanced paramedic was treating both patients with the utmost professionalism and care, while waiting for the ambulance to arrive to take both patients to hospital.
"St John will always endeavour to reach patients in the quickest possible time. However, when all ambulances are attending other medical emergencies and accidents, there will occasionally be delays. In cases like this, qualified ambulance officers will attend even if they are not driving an ambulance."
A new ambulance station had been established in Hillside Rd to cater for the increased demand from the ageing South Dunedin population, with the service "resourced adequately to meet the demands of the community", she said.
Senior Sergeant Steve Aitken said it appeared one of the vehicles had pulled out in front of the other vehicle.
